An air-circulating cooling fan for an automotive engine of, for example, the water-cooled type is driven by the crankshaft of the engine through suitable power transmission means such as a fluid coupling or by a vehicle-mounted motor. The major intents of such a fan include positively promoting passage of air through the water-cooling radiator of a vehicle and circulating air around the engine body positioned on the leeward side of the fan. Promoted passage of air through the radiator enhances the heat exchange performance of the radiator through which cooling water for the engine is to be circulated to reject heat to the atmosphere. The air forced to flow around the engine cools the engine body and other associated members subjected to the attack of the heat generated by the engine during operation of the automotive vehicle.
The vane structure of a known air-circulating cooling fan used for such a purpose is designed so that the fan functions as a compromise between a centrifugal fan and an axial-flow fan so as to be capable of delivering large draught volumes or high rates of volumetric flow with high pressures for given duties.
One of the prominent problems encountered in a priorart fluid propeller fan of this nature is that suction tends to be developed around and in the neighbourhood of the axis of rotation of the wheel rotor of the fan. The suction thus built up around the vane-carrying hub of the fan wheel rotor draws air toward the hub from the leeward side of the fan and, as a consequence, causes reduction in the volume of the draught to be ultimately delivered from the fan. The reduction in the amount of draught available of an air-circulating propeller fan for a given duty gives rise to a decrease in the performance efficiencies of the fan and further to deterioration in the quiet-operating characteristics of the fan for increased duties when the fan is used, particularly, as a cooling fan for an automotive internal combustion engine.
The present invention contemplates elimination of these drawbacks inherent in a conventional fluid propeller fan of the type designed as a compromise between a centrifugal fan and an axial-flow fan.
It is, accordingly, an object of the present invention to provide an improved fluid propeller fan capable of delivering increased draught volumes or rates of volumetric flow for any given duties.
It is another object of the present invention to provide an improved fluid propeller fan which features an increased performance efficiencies and excellent quiet-operating characteristics.
It is still another object of the present invention to provide an improved fluid propeller fan providing advantages of both of a centrifugal fan and an axial-flow fan and nevertheless free from development of suction around and in the neighbourhood of the axis of rotation of the fan wheel rotor thereof.